1. Field of the Invention
This invention relates to an apparatus for monitoring a fluid pressure through the utilization of one or more Bourdon tubes having an open end in fluid communication with a fluid pressure source to be monitored and a closed end operatively connected to a linearly shiftable actuator, such as the stem of a pilot valve.
2. Description of the Prior Art
Bourdon tubes have long been known in the prior art and utilized for the monitoring of fluid pressure. See, for example, the disclosures of U.S. Pat. Nos. 3,126,519, 3,145,359, 3,147,623, 3,188,419 and 3,204,464. In the majority of prior art applications of Bourdon tubes, the open end of the tube is connected to a fluid pressure source to be monitored and the closed end of the tube is employed to shift an actuating or indicating arm in a circular path, for example, the arm of an electric potentiometer which thus generated an electrical signal proportional to the changes in the fluid pressure being monitored. As is well known, the Bourdon tube depends to a high degree for its accuracy in detecting changes in fluid pressure to the unrestrained mounting of the turns of the tube. Every Bourdon tube responds to a change in applied fluid pressure by either a radial expansion or contraction of the turns of the tube which results in the closed end of the tube moving in a generally circumferential path which can be readily translated into a rotational or linear movement of an actuator or an indicator.
When it is desired to employ a Bourdon tube to effect the shifting of a linearly shiftable actuator, or indicator, the mechanisms heretofore disclosed in the prior art have not provided the capability to increase the force output of the closed end without decreasing the total available movement of the tube tip, particularly not in conjunction with the ability to adjust the stressing of the Bourdon tube for calibration purposes. Common ways to obtain increased force are to use fewer number of coils in the tube or a mechanical lever. Both ways reduce the movement of the tip for a decrease or increase in the pressure being sensed.